How stable is trunk and is it ready for production use? Compatibility of modules would be a concern as my site's making heavy use of them.

Can I suggest that documentation (both normal and API docs) is versioned? That way it becomes clear what's usable in trunk and what's usable in the 'stable' 2.3 release. The Kohana team had this issue, and they've adopted a similar approach to Symfony & Doctrine with their documentation.